1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having a power supply switch cell that controls supplying of supply voltage or reference voltage to a circuit cell and blocking of the voltage supplying.
2. Description of Related Art
To control supplying of supply voltage or reference voltage to a circuit cell and blocking of the voltage supplying is known as, for example, a circuit technique called multi-threshold complementary metal oxide semiconductor (MTCMOS). In the MTCMOS, for example, for each circuit block having a specific function, a power supply switch transistor with threshold voltage higher than that of a transistor in a functional circuit is connected to the path of the supplying of the supply voltage or the reference voltage (e.g. GND voltage). When the circuit block enters the unused state, the power supply switch transistor is set to the off-state, so that the leakage current that flows through the respective transistors in the circuit block is blocked. This can significantly reduce the leakage current that flows through the circuit block in the unused state.
For the purpose of eliminating a troublesome task of arranging power supply switch transistors based on manpower in design of a semiconductor integrated circuit including a circuit block to which the MTCMOS technique is applied, the inventors of the present application have already proposed a semiconductor integrated circuit in which power supply switch transistors are included as cells and the power supply switch cells are properly disposed in the area in which circuit cells are arranged (refer to Japanese Patent Laid-open No. 2005-259879 (hereinafter referred to as Patent Document 1)).